Effect of adaptive rootzone development in quantitative land evaluation studies

For quantitative land evaluation studies often simulation models are used to determine differences between soil types in terms of water availability (actual transpiration) or crop productivity. In the Netherlands we developed a land evaluation system specifically for water authorities, provinces and drinking water companies. The system allows answering questions on how water management influences crop development due to too dry or too wet conditions in the unsaturated zone. This system is based on the linked simulation model SWAP (Soil-Water-Atmosphere-Plant) and WOFOST (WOrld FOod STudies). The impact of changes in climate or hydrology can then be studied in terms of effects on crop growth and farm income.

Although SWAP and WOFOST are process based models, the rootzone development is simulated in a straightforward way: the development of the root extension is specified by the user in advance and the root length density distribution is assumed static in time. Roots play a key role in the interaction between soil water and crop growth and crop yield simulation. Although plant roots are highly adaptable, their adaptability is often neglected in simulation models that are used for predicting impacts on yield. For a more realistic approach we implemented a simple and innovative root growth model which will react on the hydrological conditions within the rootzone. This means that newly formed roots will be assigned to regions where there is no or the least stress, and less or no new roots to regions where water stress was experienced. As a result the drought and oxygen stress will be less dependent on the initial root distribution as specified by the user.

The model performance of the adaptive root growth model is compared with a rhizobox experiment where the root growth of maize was tracked while influencing soil moisture conditions at the same time (Maan et al., 2023). An example for a regional study will be provided to show the relevance of adaptive rootzone development for assessing land qualities in space and time.